Recent work of this laboratory shows that separation of infant rats from their dam for periods of 6 to 8 hours predisposes them to increased NaCl intake in adulthood. The increased intake is expressed both when the animals are sodium deficient and when they are need-free. That is, they drink more 3% NaCl both in the immediate aftermath of acute sodium depletion and while they are in positive sodium balance and have no meta- bolic need for the ingested sodium. The elevated need-free salt intake persists for the life of the animal, and is greater in females, despite the ingestion of sodium-rich commercial food, and despite the absence of renal pathology or of alterations in the plasma levels of the hormones of renal sodium conservation (angiotensin 11 and aldosterone). It is, in other words, an animal model of chronic salt overconsumption in man. The proposed experiments will investigate the biological basis of the phenomenon by: 1. Specifying the most effective aspect of the maternal separation. 2. Describing the age of its onset. 3. Testing the adult consequences of repeated neonatal treatments. 4. Testing the possibility that it is a result of the operation in infancy of the angiotensin/aldosterone synergy that is the basis of salt appetite in the adult rat. 5. And, continuing the studies of the suppression of salt intake by the tachykinins with emphasis on the ontogeny of their antinatrorexic effects. This research is relevant to a significant public health and medical problem. Sodium overconsumption is common in our population. A lifetime of excess salt ingestion puts cardiovascular and renal health at risk. Basic research on the ontogeny of salt intake could result in rational chemotherapies for salt overconsumption, and in improved infant nutritional practices that would discourage excess salt ingestion later in life.